As our Kelsey Whipple wrote in her post about the judgment, linked above, the court's decision on Arizona SB-1070 (it's on view below) struck down much of the measure, but secured the rights of law enforcers to "stop, interview and detain people they have 'reasonable suspicion' to believe entered the country illegally."

The U.S. Supreme Court.

Justice Anthony Kennedy wrote the majority opinion, and Roger Sherman, the campaign director for Smart Colorado, the leading No on 64 group (and chief operating officer of CRL, a powerhouse PR firm), points to what he sees as a key line with applications beyond immigration: "...the state may not pursue policies that undermine federal law."

His interpretation? "Amendment 64 is completely contrary to federal law in regard to marijuana usage," Sherman says.

Indeed, marijuana remains a Schedule 1 narcotic at the federal level, despite cannabis having been approved for medical purposes in a number of states, including Colorado. The Obama administration has allowed states to develop medical marijuana rules and regulations (something that would seem to undercut Sherman's assertion), but not without limits: Note that U.S. Attorney John Walsh has issued closure-threat letters to dozens of dispensaries located within 1,000 feet of schools regardless of whether they were following state law.

Likewise, in 2010, Attorney General Eric Holder spoke out publicly against Proposition 19, a California marijuana legalization measure, shortly before voters had a chance to weigh in on it. After Holder declared that the federal government would "vigorously enforce" its laws against anyone found to be carrying, selling or growing weed, the measure went down to defeat, prompting The Atlantic to ask, "Did Eric Holder Kill California's Pot Initiative?"

Sherman expects something similar to happen again this year. "In California, the Justice Department was pretty clear that legalization would not be tolerated," he says, "and we anticipate they would take the same position with Colorado's proposal."

Roger Sherman.

One reason, in his view, is that "there is a difference of opinion on medical marijuana. That's an exception that's reasonable. And while I haven't spoken to Attorney General Holder, it certainly looked like they drew a bright line between what might be allowed within the medical marijuana framework and what would be allowed with a wide, across-the-board legalization. And that would certainly be a basis for a challenge on the constitutionality of a state constitutional amendment that flies in the face of federal law."

Not that Sherman guarantees Amendment 64 would lose in the courts: He doesn't go that far. But he stresses, "There would clearly be costs associated with any kind of challenge, and they're not the only ones. There are lots of costs associated with this proposal, including unfunded mandates to local municipalities. And there's a fairness issue for users who might believe they're free and clear and allowed to use marijuana at their leisure and pleasure -- and that's not the case.

"There are personal ramifications to this, and I don't think proponents fairly address them," he goes on, adding, "It's not a slam dunk for recreational users if this passes in Colorado."

What's attorney Brian Vicente, one of the primary proponents of Amendment 64, think of Sherman's analysis? Not much.

Page down to continue reading about Amendment 64 and the Arizona immigration ruling.

Brian Vicente.

Vicente calls the scenario Sherman sketches "a real stretch. The federal government has been clear that it's not a priority for them to come after adults using marijuana privately, and they've made it clear it's not a priority for them to come after regulated marijuana sales in Colorado's medical marijuana market.

"So the No on 64 campaign is engaging in what we've seen for the past eighty years -- fairly baseless scare tactics. They're trying to threaten Colorado voters -- trying to scare them into moving away from what they truly believe. We think more and more Coloradans understand that marijuana should be regulated and taxed, and that the state will be a safer place, with larger tax coffers, when this passes."

By and large, Vicente notes, "the feds have had a hands-off approach to medical marijuana dispensaries in Colorado. They've been active in some of the zoning issues, trying to shut down dispensaries they feel are in the wrong zone. But they've respected the will of the state legislature and the state voters to decide on their own medical marijuana policies, and we believe they'll do the same for a broader adult market."

A court challenge is possible should Amendment 64 win voter approval, Vicente concedes. But he thinks the way the measure is written would make such an effort difficult.

"Essentially, our initiative changes state criminal law. The only possession-related arrests that take place in Colorado are prosecuted under state law, and that law would be gone. So for the federal government, for the first time in history, to flex its muscles and prosecute a 45-year-old man for possession of a small amount of marijuana is just totally implausible."

Even Sherman admits that the feds almost certainly won't go after individual marijuana users. But he thinks "what's important is the larger issue -- whether it's constitutionally legal for a state to take a position in its constitution that's directly in violation of federal law. And there are issues for employers that should raise some concerns. Does this put federal grants, federal funding, federal projects in jeopardy when there are still drug-free workplace requirements attached to those kinds of things? So there are a lot of issues around the conflict with federal law."

The bottom line from Sherman's perspective: "I think the federal government has made a distinction between medical marijuana and recreational marijuana. I think it's in a whole different category, and I would expect they would be handling it differently."